1. Field of the Invention
The present invention relates to an image reading apparatus such as a facsimile, a copying machine, and an electronic black board, a photoelectric converter to be mounted in the apparatus, and an image reading apparatus mounting the photoelectric converter and, more particularly, to a photoelectric converter in which a photoelectric converting element (photosensor) array is formed.
2. Related Background Art
In order to reduce the size of a photoelectric converter and improve the yield to reduce a manufacturing cost and the like, photoelectric converters as shown in FIGS. 1A and 1B are proposed. These converters adopt an arrangement in which a sensor substrate having a photosensor is mounted on a support (to be referred to as a packaging substrate) formed in another step.
These converters will be described in detail below.
FIGS. 1A and 1B are a schematic perspective view and a sectional view, respectively, showing conventional photoelectric converters. Referring to FIG. 1A, a ceramic substrate 1001 has a driver portion 1002, a sensor portion 1003, and a bonding gold wire 1004. Such a photoelectric converter is disclosed in, e.g., Japanese Patent Laid-Open No. 60-132452.
In the arrangement shown in FIG. 1A, however, a thick film circuit 1005 as the driver portion 1002 is formed on the insulating ceramic substrate 1001 as a packaging substrate, the photosensor array portion 1003 is fixed on the packaging substrate 1001, and the thick film circuit 1005 and the photosensor portion 1003 are connected by the gold wire 1004 by a wire bonding method. Therefore, since the packaging substrate 1001 is nontransparent, the arranging position of a light source is limited to make it difficult to achieve a sufficiently small optical system which is an advantage of an elongated sensor.
In the photoelectric converter shown in FIG. 1B, a transparent sensor substrate 1032 having a photosensor 1031 is fixed on a transparent packaging substrate 1010 by an adhesive 1070, and a mold 1080 consisting of a nontransparent resin is formed on the photosensor 1031. Information light is received by the photosensor via the transparent packaging substrate and the transparent sensor substrate. A light-shielding plate 1060 for preventing incidence of unnecessary light beams is formed on the transparent packaging substrate. A photoelectric converter having such an arrangement is disclosed in, e.g., Japanese Patent Laid-Open No. 62-97370. In this arrangement, however, information light from a document surface is incident on the light-receiving element (photosensor) through the transparent packaging substrate and the transparent sensor substrate. Therefore, an optical path of the information light to the photosensor is elongated to tend to produce a light quantity loss. In addition, a stray light component is produced due to diffusion light in each layer to tend to reduce an S/N ratio or a sensor output.
In addition to the above problems, if a light source of a photoelectric converter has a light quantity variation, a variation occurs in an output signal from a sensor, or a white or black stripe sometimes appears to cause a read error. As a technique for eliminating this drawback, an arrangement in which a light-adjusting member (lighting curtain) is provided in an optical path between a light source and a document is available. This lighting curtain is in the form of a light-shielding film formed on a film by a pattern capable of obtaining a constant light quantity distribution. Illumination light on the document surface is corrected to be uniformly distributed by the lighting curtain. This arrangement is disclosed in, e.g., Japanese Patent Laid-Open No. 63-310262.
In this conventional technique, however, since the lighting curtain is provided as an additional member, positioning precision between the lighting curtain and the light source may not be held at a high level, and the manufacturing cost is increased.
It should be noted that in a photoelectric converter, as the number of photoelectric converting elements to be arranged is increased to elongate the converter, a wiring pattern is elongated to cause mixing of electrical noise components. Generation sources of the electrical noise are a power source, static electricity generated upon document conveyance (paper passing), a light source circuit, and the like. This electrical noise induces noise in a signal output circuit and makes an image signal unstable. As a means for preventing this problem, a base plate (a box member for fixing a sensor) is held at a constant potential to provide a shielding effect of electrical noise. This shielding effect prevents the electrical noise from entering into a sensor, thereby obtaining a stable image. This arrangement is disclosed in, e.g., Japanese Patent Laid-Open No. 63-310261.
This arrangement, however, has the following problems:
static electricity generated upon paper passing when the base plate is set at a ground (GND) potential enters via the base plate, a GND line, and a driver to destroy the circuit or cause an erroneous operation;
the shielding effect can be provided to the base plate if the plate is made of a conductor such as Al, but it cannot be provided if the plate is made of an insulator such as a resin; and the like.
Japanese Patent Laid-Open No. 62-97370 discloses a method of coating a transparent adhesive on the entire surface between a transparent packaging substrate and a transparent sensor substrate. In this method, however, bubbles may be formed in the adhesive layer to cause a light quantity loss and generate a stray light component.
In addition, since a transparent adhesive which does not cause much light quantity loss, i.e, has high transparency must be selected, a degree of freedom of selection for the adhesive is decreased.
Furthermore, reduction in stress between the transparent packaging substrate and the transparent sensor substrate must be taken into consideration.